Styrenic polymers having a syndiotactic configuration (occasionally referred to as SPS hereinafter) have excellent heat stability, electric properties, and dimensional stability against moisture absorption and used for various types of high precision parts as engineering plastics. Furthermore, it has been desired that metal plated articles of SPS are developed and widely used in new fields in which plated articles of conventional acrylonitrile-butadiene-styrene copolymers (ABS) cannot be used.
Generally for plating plastic molded articles, roughness is formed on the surface of the articles by using an oxidizing agent such as chromic acid (etching), and a metal is tightly attached to the resultant surface by taking advantage of the rough structure (an anchor). In ABS which is widely used as a plastic material with plating, the butadiene part is dissolved in oxidizing agents to form the anchor because butadiene (B) is easily soluble in oxidizing agents. Therefore, the plating of ABS is easily performed.
In contrast, plating of SPS has been difficult because SPS is excellent in chemical resistance and does not have any part corresponding to that of butadiene (B) in ABS.
Generally when ABS is plated, the surface of an article is treated for formation of roughness, and after a catalyst for chemical plating is provided to the resultant surface by a combination of catalyzing and acceleration or a combination of sensitizing and activation, the surface is chemically plated, and the chemically plated surface is then electrically plated.
However, when the process described above is applied to a molded article containing SPS, problems arise in that skipped plating frequently takes place in the chemical plating, and in that a plating film having a sufficient adhesive strength cannot be obtained. Because of these reasons, no molded article having a plating film of metallic appearance has heretofore been obtained from a molded article containing SPS.
On the other hand, the plating property of plastics which do not contain any part easily soluble in an oxidizing agent, such as engineering plastics such as polycarbonates (PC) and modified polyphenylene ethers (Noryl) and general-purpose plastics such as polypropylene (PP), can be improved by blending a substance easily soluble in an oxidizing agent (Japanese Patent Application Laid-Open No. Showa 53(1978)-88876, Japanese Patent Application Laid-Open No. Showa 53(1978)-140348, Japanese Patent Application Laid-Open No. Showa 63(1988)-215760, and Japanese Patent Application Laid-Open No. Heisei 2(1990)-59178).
However, the basic physical properties of SPS, such as melting point, glass transition temperature, and rate of crystallization, the surface condition of molded articles containing SPS, and the conditions suitable for obtaining molded articles containing SPS are entirely different from those of other engineering plastics, such as PC and Noryl and general-purpose plastics, such as PP or those of molded articles containing such plastics. Therefore, it has been difficult to obtain a plated molded article having a sufficient adhesive strength of the plated film by simple application of conventional technologies.
Under the above circumstances, the present inventors undertook extensive studies to solve the above problems and to obtain a plated molded article containing SPS which has a high adhesive strength of the plating film and can be produced with stability in an industrial process.